Autodetect nocloud if CLOUD is unset

Set default CLOUD to 'auto', which will try autodetect the cloud
provider.

Each cloud can have an autodetect script which should print:
  <priority> <cloud>
if cloud was detected.

lib/tiny-cloud/cloud/nocloud/autodetect

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+# Tiny Cloud - Autodetect
+# vim:set filetype=sh:
+# shellcheck shell=sh
+
+grep -w 'ds=nocloud' "$ROOT"/proc/cmdline 2>/dev/null \
+	|| grep -w "^ds=nocloud" "$ROOT"/sys/class/dmi/id/product_serial 2>/dev/null \
+	|| findfs LABEL=cidata >/dev/null 2>&1 \
+	|| findfs LABEL=CIDATA >/dev/null 2>&1 \
+	&& echo "10 nocloud"

lib/tiny-cloud/common

@@ -4,7 +4,7 @@
 
 # set defaults
 [ -f "$ROOT/etc/tiny-cloud.conf" ] && . "$ROOT/etc/tiny-cloud.conf"
-: "${CLOUD:=unknown}"
+: "${CLOUD:=auto}"
 : "${CLOUD_USER:=alpine}"
 : "${TINY_CLOUD_LOGS:=$ROOT/var/log}"
 : "${TINY_CLOUD_VAR:=$ROOT/var/lib/cloud}"

lib/tiny-cloud/init

@@ -37,6 +37,20 @@ DEFAULT_ACTIONS_FINAL=""
 [ ! -d "$TINY_CLOUD_LOGS" ] && mkdir -p "$TINY_CLOUD_LOGS" || true
 [ ! -d "$TINY_CLOUD_VAR" ] && mkdir -p "$TINY_CLOUD_VAR" || true
 
+# autodetect cloud
+if [ "$CLOUD" = "auto" ]; then
+	CLOUD=$(cat "$TINY_CLOUD_VAR"/.autodetect 2>/dev/null) || {
+		CLOUD=$(
+			for i in "$LIBDIR"/tiny-cloud/cloud/*/autodetect; do
+				if [ -f "$i" ]; then
+					"$i"
+				fi
+			done | sort -n | cut -d' ' -f2 | head -n 1
+		)
+		: ${CLOUD:=unknown}
+		printf "%s\n" "$CLOUD" > "$TINY_CLOUD_VAR"/.autodetect
+	}
+fi
 
 ### standard boot phase functions...
 

tests/init.test

@@ -23,7 +23,11 @@ init_tests \
 	set_hostname \
 	set_ssh_keys \
 	userdata_type \
-	run_userdata
+	run_userdata \
+	autodetect_unknown \
+	autodetect_nocloud_cmdline \
+	autodetect_nocloud_dmi \
+	autodetect_nocloud_volume
 
 PROVIDERS="aws azure gcp nocloud oci scaleway hetzner"
 
@@ -225,3 +229,40 @@ run_userdata_body() {
 	grep "hello from user-data" var/log/user-data.log || atf_fail "user-data.log failed"
 	grep -w "0" var/log/user-data.exit || atf_fail "user-data.exit failed"
 }
+
+autodetect_unknown_body() {
+	atf_check \
+		-o match:"unknown" \
+		sh -c ". \"$lib\"; echo \$CLOUD"
+}
+
+autodetect_nocloud_cmdline_body() {
+	mkdir -p proc
+	echo "quiet ds=nocloud;s=https://10.42.42.42/ console=ttyS0" > proc/cmdline
+	atf_check \
+		-o match:"nocloud" \
+		sh -c ". \"$lib\"; echo \$CLOUD"
+}
+
+autodetect_nocloud_dmi_body() {
+	mkdir -p sys/class/dmi/id
+	echo "ds=nocloud;s=https://10.42.42.42/" > sys/class/dmi/id/product_serial
+	atf_check \
+		-o match:"nocloud" \
+		sh -c ". \"$lib\"; echo \$CLOUD"
+}
+
+autodetect_nocloud_volume_body() {
+	fake_bin findfs <<-EOF
+		#!/bin/sh
+		case "\$1" in
+			LABEL=cidata) echo "/dev/sda1";;
+			LABEL=CIDATA) echo "/dev/sda2";;
+			*) exit 1;;
+		esac
+	EOF
+
+	atf_check \
+		-o match:"nocloud" \
+		sh -c ". \"$lib\"; echo \$CLOUD"
+}